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Resistors over heated (smoked) on kit (resolved)


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I put my LOR controller together from the kit and made sure everything was working a few Christmas lights. Then I put the heat sinks on, and decided to try some of the halloween lights I have. I connected 4 sets of minis on one side of the board (it's a 16 channel controller, but I only have it wired up for 8 channels (4 per side) right now) and 2 sets of minis, a light up spider web, and my 4 strobes (these ones: http://www.christmaslightshow.com/xcart/product.php?productid=54)

I plug it in and fire up the hardware controller. I then turn all the lights on, and lo and behold, they lights turn on. However, when I turn them off, all the lights turn off except for the strobes, which are still running after a few seconds. I then unplug them from the controller. I looked inside the box that I had my controller in, and to my horror I see one of the resistors in front of the triacs is on fire! :shock:

I unplug the controller and take a look at what went wrong. Everything looks fine from the top, except the 4 resistors that had things plugged into them on the side with the strobes look totally fried. The resistor on the channel that had the strobes was the one that caught fire. All the other ones look burnt up. It's a good think I unchecked the channels I wasn't using, otherwise the whole side may have been fried.

I used a C-9 string for the stobes, and didn't bother covering the empy sockets yet, as I was just testing them.

I know that the LOR board says it can only be used with Incandescent, but people have been using them with strobes right? Did I do anything wrong?

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Yep, they work just fine. I tested them earlier, then placed all the regular C9 bulbs back into the string when I was done. When I decided to test them on the controller, I took out all the C-9 bulbs and put my strobes in and connected it to my controller. I did notice that a few were not working when I turned on the board, but that was because they weren't in tight enough. The strobes still work if they are plugged into a regular outlet.

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Assuming your test with strobes was the first test for that controller, I'm sure it was just a coincidence, and the strobes had nothing to do with it. You probably don't want to prove that theory by plugging them into another channel now, though...

At least resistors are cheap -- hopefully that's all that needs changing out. Carefully check all your solder joints and make sure nothing is bridged, and that nothing has a bad joint (commonly called a "cold solder joint"), they can generate heat.

-Tim

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I can't really say what the problem is, but the resistors wouldn't have burnt on their own - something had to be feeding too much current through them. On the other hand, they aren't connected to the load either, so the load wouldn't have fried them. My guess is some other component is bad (triac or possibly an opto), or there is a short somewhere (something touching board, or two pins bridged by solder somewhere.

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Yeah, since you put together the board yourself, it almost definitely sounds like a short. Strobes draw very little current.

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Thanks for the suggestions. Looks like I'll be taking the heatsinks off my board and taking a good look at it. If it is a bad triac or opto, do I have to order a new one from LOR, or can I get those at RadioShack?

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Radio shack used to carry an opto and triac that would work, although there selection of electronic components (and anything else usefull, for that matter), has steadily decreased, so I don't know at this point.

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Talk to Dan about it. LOR has an unconditional lifetime replacement policy, so you can get a new kit at 40% off the list price. It may be worthwhile just to guarantee no other damage was done to any other components on the board.

*Edit* Grammar

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Can you say major short? After looking at my board, I found this:

shortlw0.th.jpg

Looks like I'll need some new Traics and resistors. Possibly ICs, but we'll have to see. The leads for the triacs weren't cut, and are contacting the heatsink, creating a MAJOR short. Not good. Do you think I would need anything else beside resistors and Triacs?

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You mentioned adding the heatsinks..and then having this happen...I had wondered about something shorting out against the metal possibly.
But WOW!!!

I am sure the excitement of getting it completed is what caused you to overlook trimming those leads...

Hopefully after replacing some componants you will be get things working again.

Be carefull if the PC board itself is blackened... it can turn to carbon and become conductive.. and result in a short circuit through the board material!

This goes for all us DIY people..we are dealing with line voltage on our displays and controls... always force yourself to stop and take the time to check things over carefully (2 or 3 times even!) before powering up...:(

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Just an update: I was able to go to Radioshack and pick up some resistors. It took a while to desolder the fried ones, but I got the new ones soldered on and everything seems to be wroking fine. :waycool:

I also clipped the leads for the triacs :) I can't beleive I missed that. Anyways, I also picked up some heatsink compound to put on the triacs and heatsink, the compund on there already got mostly wiped off.

Thanks for the help! Now I need to find where to get an Orbit case....

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Erik Sommer wrote:

Just an update: I was able to go to Radioshack and pick up some resistors. It took a while to desolder the fried ones, but I got the new ones soldered on and everything seems to be wroking fine. :waycool:

I also clipped the leads for the triacs :) I can't beleive I missed that. Anyways, I also picked up some heatsink compound to put on the triacs and heatsink, the compund on there already got mostly wiped off.

Thanks for the help! Now I need to find where to get an Orbit case....


Great news! Glad it was a pretty cheap fix.

-Tim
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Glad to hear about another problem solved! So what happened? Bad part? Strobe? The triac leads touching? Anything we need to know about strobe lights on LOR?




--Daniel L

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Nope, I forgot to trim the leads on the Triacs, so the Triac leads were touching the heatsinks, creating a major short. I'm glad I only had a few channels on. After I replaced the resistor, everything worked fine (as far as I can tell) and the strobes do work with LOR.

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Yep, I sometimes wait to trim leads until I'm sure everthing is in place correctly. Very important step to cut off those extranious conductors. (PS....be sure tow sweep those buggers up when done as they stick right through your socks into the fleshy part of your foot...LOL

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